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Verdemont Ranch Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Verdemont Ranch Observatory clear sky chart from 2005-11-05 to 2017-09-10.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
49%
15843
28%
46810
16%
15800
60%
15800
42%
24607

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
41%
870
30%
2476
16%
865
56%
865
50%
1169
January16th to endNight
43%
768
35%
2496
21%
768
61%
768
48%
1119
February1st to 15thNight
34%
700
25%
2241
13%
699
49%
699
40%
1139
February16th to endNight
31%
632
36%
1894
11%
632
55%
632
46%
935
March1st to 15thNight
42%
720
29%
2082
13%
720
55%
720
46%
1045
March16th to endNight
41%
696
30%
2040
14%
696
56%
696
43%
1055
April1st to 15thNight
37%
539
25%
1798
14%
539
52%
539
35%
901
April16th to endNight
38%
540
25%
1800
14%
540
54%
540
30%
989
May1st to 15thNight
42%
540
20%
1685
12%
540
52%
540
30%
991
May16th to endNight
47%
562
21%
1497
9%
561
57%
561
38%
849
June1st to 15thNight
59%
540
24%
1440
15%
540
65%
540
47%
755
June16th to endNight
68%
540
23%
1440
17%
540
73%
540
46%
784
July1st to 15thNight
67%
510
15%
1360
13%
510
68%
510
29%
896
July16th to endNight
72%
564
13%
1519
14%
531
73%
531
27%
1008
August1st to 15thNight
69%
539
14%
1677
14%
536
70%
536
28%
1026
August16th to endNight
71%
573
21%
1910
24%
573
73%
573
31%
1123
September1st to 15thNight
68%
525
24%
1750
23%
525
73%
525
33%
996
September16th to endNight
64%
500
34%
1768
27%
500
75%
500
45%
818
October1st to 15thNight
58%
660
32%
1980
21%
660
66%
660
47%
999
October16th to endNight
57%
704
38%
2112
20%
704
71%
704
53%
997
November1st to 15thNight
52%
861
35%
2261
17%
861
62%
861
56%
1128
November16th to endNight
47%
900
38%
2376
18%
900
60%
900
57%
1178
December1st to 15thNight
36%
900
26%
2520
10%
900
50%
900
47%
1271
December16th to endNight
33%
960
28%
2688
11%
960
48%
960
40%
1436

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
35%244245%6%8%51%
47819
Night
241332445%8%58%
46993
TransparencyDay
28%5%13%24%21%6%
47503
Night
22%5%15%28%22%6%
46811
SeeingDay
8%13%26%27%18%5%
5733
Night
49%29%34%18%3
15848

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
31243346%8%60%
1471
16th to endDay
42331325%9%63%
1728
February1st to 15thDay
5%36%32245%10%55%
1619
16th to endDay
5%2342446%10%56%
1580
March1st to 15thDay
16%2442446%9%52%
1875
16th to endDay
27%3433446%8%51%
2182
April1st to 15thDay
37%24435%5%6%8%50%
2150
16th to endDay
6%10%245%345%6%7%43%
2160
May1st to 15thDay
7%8%35%5%45%46%7%40%
2262
16th to endDay
5%4245%36%6%5%8%47%
2616
June1st to 15thDay
4323426%5%7%8%50%
2520
16th to endDay
2213435%6%7%8%54%
2520
July1st to 15thDay
7%435%6%36%6%6%8%40%
2520
16th to endDay
6%427%7%48%7%8%9%32%
2542
August1st to 15thDay
7%5%36%8%46%5%6%9%35%
2272
16th to endDay
7%5%25%5%25%5%6%8%44%
2292
September1st to 15thDay
6%4145%35%6%5%8%46%
2097
16th to endDay
3312324345%64%
1860
October1st to 15thDay
4213323447%60%
1650
16th to endDay
3314313347%64%
1760
November1st to 15thDay
313222348%67%
1586
16th to endDay
1223222327%68%
1581
December1st to 15thDay
32431235%10%60%
1440
16th to endDay
131432346%8%58%
1536
January1st to 15thNight
31122436%6%67%
2476
16th to endNight
311212348%68%
2496
February1st to 15thNight
6%25%422346%61%
2231
16th to endNight
33331345%9%62%
1894
March1st to 15thNight
16%2321336%8%60%
2082
16th to endNight
25%1321345%8%61%
2040
April1st to 15thNight
26%2322345%8%57%
1798
16th to endNight
49%23424446%52%
1800
May1st to 15thNight
6%7%343245%5%6%48%
1684
16th to endNight
5%5%12225%5%5%8%54%
1497
June1st to 15thNight
223225%45%8%62%
1440
16th to endNight
2312425%5%6%8%57%
1440
July1st to 15thNight
7%6%246%45%7%6%8%40%
1440
16th to endNight
4436%6%37%7%7%10%36%
1624
August1st to 15thNight
4425%6%36%5%7%9%43%
1686
16th to endNight
5%4136%35%7%6%11%43%
1910
September1st to 15thNight
6%5%146%3446%9%46%
1750
16th to endNight
432313346%65%
1768
October1st to 15thNight
33231345%7%64%
1980
16th to endNight
2322214245%66%
2112
November1st to 15thNight
121121236%8%68%
2261
16th to endNight
1411112346%70%
2376
December1st to 15thNight
31232335%8%63%
2520
16th to endNight
132431346%9%58%
2688

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
19%320%33%20%2
1472
16th to endDay
19%214%33%22%6%
1728
February1st to 15thDay
24%417%32%17%4
1620
16th to endDay
22%312%30%25%4
1580
March1st to 15thDay
26%313%24%26%5%
1875
16th to endDay
28%411%30%21%3
2182
April1st to 15thDay
28%413%27%19%6%
2150
16th to endDay
36%311%24%19%4
2160
May1st to 15thDay
39%5%12%20%18%2
2262
16th to endDay
31%5%13%21%20%7%
2620
June1st to 15thDay
26%6%13%18%21%13%
2520
16th to endDay
23%6%10%20%26%13%
2520
July1st to 15thDay
37%7%15%17%15%6%
2371
16th to endDay
39%9%19%21%7%1
2384
August1st to 15thDay
42%7%14%16%14%4
2257
16th to endDay
35%5%14%23%17%3
2292
September1st to 15thDay
31%7%14%19%19%7%
2097
16th to endDay
19%411%24%32%7%
1860
October1st to 15thDay
24%49%26%29%5%
1650
16th to endDay
19%29%29%33%6%
1760
November1st to 15thDay
16%312%23%34%9%
1586
16th to endDay
16%37%34%29%8%
1581
December1st to 15thDay
19%420%31%19%3
1440
16th to endDay
22%7%20%29%14%5%
1536
January1st to 15thNight
15%320%33%24%2
2476
16th to endNight
15%413%35%24%6%
2496
February1st to 15thNight
25%217%32%17%4
2241
16th to endNight
18%412%31%26%5%
1894
March1st to 15thNight
20%314%31%26%3
2082
16th to endNight
21%5%12%33%25%2
2040
April1st to 15thNight
24%413%30%22%5%
1798
16th to endNight
31%412%28%18%4
1800
May1st to 15thNight
33%6%13%24%17%4
1685
16th to endNight
26%5%19%24%16%7%
1498
June1st to 15thNight
18%6%15%21%20%17%
1440
16th to endNight
22%5%12%21%22%15%
1440
July1st to 15thNight
38%8%16%18%11%7%
1360
16th to endNight
35%12%21%20%6%2
1519
August1st to 15thNight
34%8%20%18%12%5%
1677
16th to endNight
31%8%18%23%14%3
1910
September1st to 15thNight
31%6%17%22%15%7%
1750
16th to endNight
20%311%27%29%6%
1768
October1st to 15thNight
20%412%26%28%7%
1980
16th to endNight
17%38%28%35%6%
2112
November1st to 15thNight
12%6%12%28%28%11%
2261
16th to endNight
15%38%33%29%9%
2376
December1st to 15thNight
18%420%31%21%2
2520
16th to endNight
21%6%19%29%19%4
2688

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
416%28%28%16%4
90
16th to endDay
37%34%41%13%
96
February1st to 15thDay
420%40%31%4
90
16th to endDay
6%16%39%24%13%
81
March1st to 15thDay
7%21%33%26%9%1
165
16th to endDay
12%29%38%13%4
288
April1st to 15thDay
12%30%30%17%7%1
269
16th to endDay
18%34%27%16%3
270
May1st to 15thDay
12%17%30%26%9%3
363
16th to endDay
8%15%29%25%17%4
517
June1st to 15thDay
414%25%26%22%7%
495
16th to endDay
35%25%27%28%9%
495
July1st to 15thDay
9%416%30%28%10%
475
16th to endDay
7%39%37%32%10%
401
August1st to 15thDay
10%223%33%22%7%
315
16th to endDay
9%420%38%19%6%
332
September1st to 15thDay
8%8%31%29%16%5%
294
16th to endDay
46%29%28%22%7%
145
October1st to 15thDay
211%16%26%32%11%
90
16th to endDay
9%11%19%27%27%5%
96
November1st to 15thDay
7%21%30%30%11%
90
16th to endDay
6%20%36%27%8%
90
December1st to 15thDay
318%47%27%2
90
16th to endDay
217%48%26%41
96
January1st to 15thNight
214%37%31%11%2
870
16th to endNight
112%38%35%9%1
768
February1st to 15thNight
29%45%34%6%
704
16th to endNight
12%50%30%5%
632
March1st to 15thNight
311%36%35%11%1
720
16th to endNight
411%39%35%8%
696
April1st to 15thNight
5%17%37%31%8%
539
16th to endNight
8%14%32%34%9%
540
May1st to 15thNight
7%11%30%37%12%1
540
16th to endNight
8%11%26%34%17%2
563
June1st to 15thNight
37%23%40%22%2
540
16th to endNight
2416%38%34%3
540
July1st to 15thNight
9%15%34%41%7%
510
16th to endNight
5%1130%51%9%
564
August1st to 15thNight
5%2435%41%9%
539
16th to endNight
5%27%33%42%8%
573
September1st to 15thNight
7%212%39%29%9%
525
16th to endNight
45%20%36%27%6%
500
October1st to 15thNight
47%24%40%18%4
660
16th to endNight
36%26%37%20%4
704
November1st to 15thNight
19%32%35%17%2
861
16th to endNight
49%36%34%13%1
900
December1st to 15thNight
212%45%30%7%1
900
16th to endNight
216%42%28%8%1
960
Page generated at 2017-09-11 17:35:27. Version ac04

Copyright 2017 A. Danko


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